At the end of the exam, you have to post your work on moodle.

Please post a tgz file. You can generate it with:

For now, only one thread performs all the computation. Modify the program so that the main function creates nb_threads threads, and each thread calls the monte_carlo_pi function nepochs / nb_threads times.

The main function should wait until all the thread finished their computation before printing the approximate value of Pi.

By running the computation in parallel, some data structures may be modified concurrently. Make sure that the computation remains correct.

Add a comment at the beginning of pi.c to justify the synchronization method that you chose.

First, modify the main function so that it opens the file filename, read each line with fgets. For each line of the file, call the function void word_count(char* line).

The word_count function splits a line into a group of words, and calls void update_word(char* w) for each word. update_word has to update the statistics (the number of time this word appears in the text) of a word. The list of know words is stored as a linked list named word_list.

Implement update_word. This function should:

• Iterate through the list word_list and search for word w;
• If w is found, increment the count of the world and return;
• If w is not in the list, allocate a new struct word_stat and initialize it with w before inserting it into the word_list list.

After processing the file, the main function calls void print_words(). This function should browse the word_list list and print each known word and its count.

Implement the print_words function.

In this question, we modify the program to make it parallel. Before starting, copy your word_count.c to word_count_parallel.c and work on this new file. This will prevent you from destroying all your hard work from the previous questions !

Modify word_count_parallel.c to set up a worker-slave processing of the file. The main function should create a set of 4 worker threads. Then when reading the file, instead of calling word_count directly, the main thread should "send" the line to a worker thread. When a worker thread receives a new line, it processes it by calling word_count, and wait for the next line.

After sending all the lines to the worker threads, the main thread notifies them that there is no more work and it waits for the end of the worker threads. The main threads can then can print_words to display the results.

Add a system call int alloc_page(void* addr) in xv6 that allocates a memory page, fills it with zeros, and maps it at address addr.

The system call return 0 if successful, or -1 in case of an error.

Add a system call int free_page(void*addr) that free a memory page allocated with alloc_page.

Create a test program test_alloc.c. This program allocates 10 memory pages, write some data in the allocated pages (for example 1), and free the memory pages.